The relative speed of airflow varies with the distance away from the surface. Right next to the surface there is no measurable relative motion. The thin boundary layer is slowed down by the presence of the surface.

A layer of fluid, close to the surface of a body placed in a moving stream, that is distinguishable from the main airflow by distinctive flow characteristics of its own caused by friction Glossary Index

a transition layer between two neighboring regions in the magnetosphere. The plasma sheet boundary layer (PSBL) is the transition from the plasma sheet and the tail lobes. The low latitude boundary layer (LLBL), just inside the magnetopause, is the transition between the equatorial magnetosphere and the solar wind (more accurately, the magnetosheath, solar wind slowed down by passage through the bow shock).

a gradient in velocity that results from a fluid’s viscosity (“internal stickiness”) and the “no slip condition,” a phrase used to describe the tendency for a fluid to adhere to a solid surface. The thickness of the boundary layer provides an estimate of the distance any substance, such as an oxygen molecule, has to travel in order to move between the water column and a benthic organism. ( return to essay)

A layer of static to slow moving air adjacent to the surfaces of a moving body. Friction between the body and the surrounding air holds back the flow nearest the surfaces, whilst the air further from the body in the mainstream flows past at unabated speed.

A layer of fluid near a surface, where flow is affected by viscous properties of the fluid. At the surface, fluid velocity must be zero, and the boundary layer is a thin film that depends on surface texture, fluid velocity in the "mainstream of flow," and fluid mass properties such as salinity.

The air in immediate contact with a fuel particle. That part of the lower atmosphere that is directly influenced by the presence of the earth's surface and responds to surface forcings with a time scale of about an hour or less.

The region close to a surface in which the air velocity varies from zero at the surface up to its full value (in the main stream). Outside the boundary layer the fluid moves at the full velocity, and may be considered in practice to be unaffected by the reduction of velocity close to the surface.

The thin layer of air immediately surrounding the surfaces of an aeroplane or airship. This layer is slowed down in flight by the friction exerted on the surface as it moves through the air and represents an important element of drag.

in general, a layer of air adjacent to a bounding surface. Specifically, the term most often refers to the planetary boundary layer, which is the layer within which the effects of friction are significant. For the earth, this layer is considered to be roughly the lowest one or two kilometers of the atmosphere. It is within this layer that temperatures are most strongly affected by daytime solar heating and nighttime radiational cooling, and winds are affected by friction with the earth's surface. The effects of friction die out gradually with height, so the "top" of this layer cannot be defined exactly.

The lowest layer of the earth's atmosphere, usually up to 3,300 feet, or one kilometer, from the earth's surface, where the wind is influenced by the friction of the earth's surface and the objects on it. Related terms: surface boundary layer and friction layer

An area in the troposphere which is affected by the solar heating, radioactive cooling, and surface friction of the earth. The height of the boundary layer can range anywhere from 100m to 300 km and coincides with the height at which pollutants are mixed. [Journal of Applied Meteorology; v28, pages 885-903; 1989] [Atmospheric Environment; v37n16; pages 2193-2205; 2003

1. The layer of fluid near a boundary that is affected by friction against that boundary surface, and possibly by transport of heat and other variables across that surface. In meteorology, this is the atmospheric boundary layer. 2. In a physical or mathematical system, a region over which some property or term in the equations varies rapidly, that is, over its full range; conversely, a region outside of which certain terms may be neglected.

In physics and fluid mechanics, the boundary layer is that layer of fluid in the immediate vicinity of a bounding surface. In the atmosphere the boundary layer is the air layer near the ground affected by diurnal heat, moisture or momentum transfer to or from the surface. On an aircraft wing the boundary layer is the part of the flow close to the wing.